Ghafir: (21) Have they not traveled in...
{They were stronger than them}
Question: It is a rule that the faṣl (pronoun of separation) should only occur between two definite nouns. Why, then, does it occur here between a definite noun (hum) and an indefinite one (ashaddu minhum)?
Answer: The indefinite noun has come to resemble a definite one in that it does not accept the definite article (al-), and thus it is treated as if it were definite.
It is also recited as: {from you} (minkum), which is the reading in the codices of the people of Syria.
{And traces}
He means their fortresses, palaces, and equipment, and whatever is described as strong among their remains. Or, he means: "more numerous in traces," as in the poet's saying:
Wearing a sword and a spear.
{And We certainly sent Moses with Our signs and a clear authority * To Pharaoh, Haman, and Korah; but they said, "A sorcerer and a liar." * And when he brought them the truth from Us, they said, "Kill the sons of those who have believed with him and keep their women alive." But the plan of the disbelievers is not except in error.}